Newly elected Democratic mayor Arturo Garino was busy with Election Day when the Army arrived in Nogales and started erecting coils of glistening razor wire along the tops of the border wall that separates his small U.S. town from its sister in Mexico.

"Razor wire, concertina wire is not what you want to see on a fence with two countries that have been friends and traded forever," he said.

"And now here we have a wire, you know, downtown, el puro downtown," Garino said.

Arizona immigration officials say troops are necessary to support CBP and ensure orderly crossings, especially as a large caravan of mostly Central American migrants approach the border. But some residents and local officials say say they're not needed.

The military action is called Operation Secure Line; the original monicker, Operation Faithful Patriot, was dropped shortly after the troops' arrival to the Southwest border.

Col. Larry Dewey, commander of the 16th Military Police Brigade from Fort Bragg, N.C., and his counterparts in CBP explained Friday that the main reason for the military buildup was the caravan of migrants making its way to the border from Mexico.

Rodolfo Karisch, chief of the Border Patrol's Tucson Sector, says that "over the last few years, we have seen significant increases in the number of Central American families and unaccompanied children who have been arriving at our border. It's been dramatic increases for us," he said.

At some points on the border, he said illegal crossings have doubled.

"The status quo is not sustainable. We're all seeing huge increases of people arriving, and we haven't even started to talk about the caravan," he said.

Worries about migrants rushing the border

The migrants reportedly intend to seek asylum further west in Tijuana. By Friday, CBP had brought in pallets of children's cereal, animal crackers, baby wipes and diapers to prepare for the migrants should they come to Nogales. And they have coordinated with northern Mexico officials and charities in the U.S. to help care for them. But officials worry migrants will try to storm the border.

Petra Horne is acting director of CBP's Tucson field office.

"Our goal is, if individuals are here to seek asylum, they need to do so in an orderly fashion," she said.

Horne said this caravan could pose a different risk than the caravan that arrived last April, which sparked tweets from President Trump and the mobilization of National Guard troops to the border. Despite concerns, 93 percent of the migrants on that caravan passed a credible-fear interview with CBP and were allowed into the country to continue the asylum process.

When asked why the deployment is happening now, Horne said, "Well, I can tell you that in Nogales where we sit today, we have had multiple groups trying to run through our vehicular lanes so it is already happening. We're wanting to get the message out in advance to warn these individuals not to do that."

'A nervous psychosis'

A CBP spokesperson said last week six families all attempted to run into the U.S. through vehicle lanes within 24 hours. Pedestrian lanes are carefully gated and can easily be controlled whereas open vehicle lanes are wide open.

Standing on a street corner in downtown Nogales, Vicente Valdez was talking about the buildup with a friend. He is a U.S. citizen who was born in Mexico.

"The U.S. has the right to secure its border," he said in Spanish, "but it's turning that into a nervous psychosis."

At the Santa Cruz County building in Nogales, Supervisor Bruce Bracker said the military presence is a classic symptom of Washington, D.C. not working with local officials.

"If they'd come down and asked people on the southern border what is it that you need, we would tell them. we need personnel for customs and we need personnel for Border Patrol."

At the port, carrying two heavy shopping bags, Mexico resident Alicia Romero prepared to cross back to her home.

"Crossing the border can take two, three hours," she said. Like Bracker, she'd prefer the U.S. spend its resources speeding up border crossings for visitors like her.